Garmin Express won't open on windows 8

Run the Windows Compatibility Troubleshooter on the executable.

It doesn't open at all

I have the same with Windows 10 nothing helps

GE doesn't have to open to run the Compatibility Troubleshooter tool.  I'm not familiar with Windows 8 but follow the steps at https://windowstechies.com/steps-in-using-the-program-compatibility-troubleshooter/ and see what method might be easiest for you to run the tool 

The problem remains

If you are familiar with the Windows registry, you might want to try a brute force uninstall, then reboot your PC, download the current version and then reinstall.  The steps to completely remove the GE related registry entries are at support.garmin.com/.../  

Oxygene, have you ever had Garmin Express function properly?  If not are you running a Windows 10 PC in "S" mode?  To check, go to Settings > System > About. On the About page, scroll down to the “Windows Specifications” section. If you see the words “in S mode” to the right of the Edition entry, you're using an S Mode PC. If you don't, you're not using S Mode.